Multilayer wiring board and method for manufacturing the same

ABSTRACT

A wiring board including a main substrate having a base material and a conductive pattern formed on the base material, and a flex-rigid printed wiring board provided to the main substrate and having a rigid substrate and a flexible substrate connected to each other. The flex-rigid printed wiring board has a conductive pattern formed on the rigid substrate and/or the flexible substrate. The conductive pattern of the main substrate is electrically connected to the conductive pattern of the flex-rigid printed wiring board.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefits of priority to U.S.Application No. 61/071,789, filed May 19, 2008. The contents of thatapplication are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to a wiring board and its manufacturingmethod.

2. Discussion of the Background

An example of a multilayer wiring board and its manufacturing method isdescribed in Japanese Patent No. 3795270. Also, a flex-rigid printedwiring board, part of whose substrate is rigid and another part isflexible, is described in, for example, Japanese Patent Laid-OpenPublication H7-193370. The contents of these publications areincorporated herein by reference in their entirety.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a wiring boardincludes a main substrate having a base material and a conductivepattern formed on the base material, and a flex-rigid printed wiringboard provided to the main substrate and having a rigid substrate and aflexible substrate connected to each other. The flex-rigid printedwiring board has a conductive pattern formed on the rigid substrateand/or the flexible substrate. The conductive pattern of the mainsubstrate is electrically connected to the conductive pattern of theflex-rigid printed wiring board.

According to another aspect of the present invention, a method formanufacturing a wiring board includes forming a main substrate having abase material and a conductive pattern formed on the base material,forming a flex-rigid printed wiring board provided to the main substrateand having a rigid substrate and a flexible substrate connected witheach other, the flex-rigid printed wiring board having a conductivepattern formed on the rigid substrate and/or the flexible substrate, andelectrically connecting the conductive pattern of the main substrate andthe conductive pattern of the flex-rigid printed wiring board.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view showing a structure of a multilayerwiring board according to an embodiment of the present invention;

FIGS. 2A and 2B are views showing a part of the multilayer wiring boardshown in FIG. 1, where FIG. 2A is a cross-sectional view of a mainsubstrate, and FIG. 2B is a cross-sectional view of a flex-rigid printedwiring board;

FIG. 3A is a view to illustrate a method for manufacturing a multilayerwiring board, showing a rigid base material on which multiple mainsubstrates are formed;

FIG. 3B is a view to illustrate a method for manufacturing a multilayerwiring board, showing a flexible base material on which multipleflex-rigid substrates are formed, and a perspective view to illustrate aproduction process of a second substrate according to the method formanufacturing the present embodiment;

FIG. 3C is a view to illustrate a method for manufacturing a multilayerwiring board, the view showing a phase in which openings are formed toarrange flex-rigid substrates in a rigid base material where multiplemain substrates have been formed;

FIG. 3D is a view to illustrate a method for manufacturing a multilayerwiring board, the view showing a phase in which openings are formed toarrange flex-rigid substrates in a rigid base material where multiplemain substrates have been formed;

FIGS. 4A-4C are views to illustrate a method for manufacturing amultilayer wiring board, the cross-sectional views showing the steps toform a main substrate;

FIGS. 5A-5I are views to illustrate a method for manufacturing amultilayer wiring board, the cross-sectional views showing the steps formanufacturing a flex-rigid printed wiring board;

FIGS. 6A-6F are views to illustrate a method for manufacturing amultilayer wiring board, the cross-sectional views showing themanufacturing steps after a main substrate and a flex-rigid printedwiring board have been put together;

FIG. 7 is a view to illustrate how to put together a main substrate anda flex-rigid substrate, the view showing the structure in which aflex-rigid printed wiring board is arranged on a surface of a mainsubstrate;

FIG. 8 is a view to illustrate how to put together a main substrate anda flex-rigid substrate, the view showing the structure in which a rigidsubstrate of a flex-rigid printed wiring board is arranged in anaccommodation section of a main substrate;

FIG. 9 is a view to illustrate how to put together a main substrate anda flex-rigid substrate, the view showing the structure in which a rigidsubstrate of a flex-rigid printed wiring board is embedded in a mainsubstrate;

FIG. 10 is a view showing an example of a modified structure of aflex-rigid printed wiring board;

FIG. 11 is a view showing another example of a modified structure of aflex-rigid printed wiring board;

FIGS. 12A and 12B are views to illustrate an example in which thedensity of conductors in a flex-rigid printed wiring board is higherthan the density of conductors in a main substrate;

FIGS. 13A and 13B are perspective views to illustrate a modified exampleof the connection method between a flex-rigid wiring board and a mainsubstrate;

FIGS. 14A and 14B are perspective views to illustrate modified examplesof the connection method between a flex-rigid wiring board and a mainsubstrate;

FIGS. 15, 16 and 17 are perspective views to illustrate modifiedexamples of the connection method between a flex-rigid wiring board anda main substrate; and

FIGS. 18A-18F are cross-sectional views to illustrate another example ofthe method for manufacturing a multilayer wiring board.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The embodiments will now be described with reference to the accompanyingdrawings, wherein like reference numerals designate corresponding oridentical elements throughout the various drawings.

Multilayer wiring board 1 according to the present embodiment has astructure as a cross-sectional view shows in FIG. 1; it has rigidsections 2, 3 and flexible section 4, and collectively functions as aflex-rigid printed wiring board.

Multilayer wiring board 1 is structured by putting together mainsubstrate 21 shown in FIG. 2A and flex-rigid printed wiring board 31shown in FIG. 2B.

Main substrate 21 is made up of core base material 211 and circuitpatterns 212, 213 formed on both surfaces of core base material 211.

Core base material 211 is formed with, for example, a non-flexibleinsulative material such as glass-epoxy resin containing an inorganicsubstance such as glass cloth or glass filler, and has opening 2111 inwhich to inset flex-rigid printed wiring board 31. Circuit patterns 212,213 are circuit patterns made of a conductor such as copper.

Flex-rigid printed wiring board 31 has flexible base material 311 andrigid (non-flexible) base material 312 positioned horizontal to flexiblebase material 311, and is inset in opening 2111 formed in main substrate21.

Flexible base material 311 is formed with an insulative flexible sheet,for example, a polyimide sheet with an approximate thickness of 20-50μm. Rigid base material 312 is set to have substantially the samethickness as flexible base material 311 and is formed with, for example,a non-flexible insulative material such as glass-epoxy resin containingan inorganic substance such as glass cloth or glass filler.

Insulation layers 313, 314 are disposed to sandwich flexible basematerial 311 and rigid base material 312. Insulation layers 313, 314cover part of flexible base material 311 and rigid base material 312 andexpose the other part of flexible base material 311.

Insulation layers 315, 316 are laminated on insulation layers 313, 314.Insulation layers 313-316 are formed by setting prepreg and have, forexample, an approximate thickness of 50-100 μm.

On both surfaces of flexible base material 311, conductive patterns 321,322 made of copper or the like. Accordingly, flexible substrate 13 isformed.

On both surfaces of rigid base material 312, conductive patterns 324made of copper or the like are formed.

Conductive patterns 324 formed on both surfaces of rigid base material312 are connected with each other by means of through-holes 325 havingplated interiors. Also, conductive pattern 326 is formed on each ofinsulation layers 313-316. Conductive patterns 324, 326 formed ondifferent layers are connected to each other by means of filled vias327.

The insulation layers, conductive (circuit) patterns and vias (viaholes) laminated on rigid base material 312 make up rigid substrate 11having multilayer conductive patterns.

Also, conductive patterns 326 formed on insulation layers 313, 314 areconnected through filled vias 328 to a tip of conductive patterns 321,322 structuring flexible substrate 13.

Insulation layers 331-334 are laminated at a tip of flexible basematerial 311 to form joint section 15. In insulation layers 331, 332,built-up filled vias 335, 336 connected to conductive patterns 321, 322are formed and connection pads 337, 338 are formed on the outermostlayers.

Main substrate 21 and flex-rigid printed wiring board 31 are positionedadjacent to each other and sandwiched by insulation layers 41, 42 asshown in FIG. 1. Conductive patterns 43, 44 are formed in insulationlayers 41, 42 and connected to the inner-layer conductive patternsthrough vias 45, 46 according to requirements.

Specifically, conductive patterns 212, 213 of main substrate 21 andconnection pads 337, 338 at joint section 15 of flex-rigid printedwiring board 31 are connected to each other through conductive patterns47, 48. Also, conductive patterns 212, 213 of main substrate 21 areconnected to each other, for example, by means of copper-platedthrough-hole 49. In doing so, conductive patterns of main substrate 21and conductive patterns of flex-rigid printed wiring board 31 areelectrically connected.

In such a structure, the wiring density (the number of layers of theconductive patterns, the density of vias, etc.) of flex-rigid printedwiring board 31 is set higher than the wiring density of main substrate21.

More specifically describing, in the structure shown in FIG. 1, thenumber of wiring layers where the conductive patterns are formed inflex-rigid printed wiring board 31 is six (6), indicating that morelayers are formed than in main substrate 21, where the number of wiringlayers formed in the region that has the same thickness as flex-rigidsubstrate 31 is two (2). Also, in flex-rigid printed wiring board 31,the existing density of conductive (circuit) patterns 324-328 oninsulation layers 313-316 is set higher than the existing density ofconductive patterns 212, 213 on insulation layer (core base material)211 of main substrate 21. Also, the average number of vias perinsulation layer formed in flex-rigid printed wiring board 31 is setgreater than the average number (0) of vias per insulation layer ofinsulation layer 211 of main substrate 21. As such, in the structureshown in FIG. 1, flex-rigid printed wiring board 31 has a higher wiringdensity than main substrate 21. In such a case, defects during themanufacturing process may tend to occur more in flex-rigid printedwiring board 31 than in main substrate 21.

According to such a structure and its manufacturing method, when defectsoccur in flex-rigid printed wiring board 31, defect-free multilayerwiring board 1 may be produced by using another defect-free flex-rigidprinted wiring board 31. Accordingly, productivity may increase comparedwith conventional ones.

Also, the rigidity of main substrate 21 is higher than the rigidity ofrigid bodies 11, 15 of flex-rigid printed wiring board 31. Therefore,highly integrated flex-rigid printed wiring board 31 is protected bymain substrate 21.

Next, a method for manufacturing multilayer wiring substrate 10 havingsuch a structure is described.

Multilayer wiring board 1 is formed by separately manufacturing mainsubstrate 21 and flex-rigid printed wiring board 31, connecting them andintegrating them.

When forming main substrate 21, for example, as shown in FIG. 4A, corebase material 211 having copper foils 221, 222 on both surfaces, forexample, a resin copper film sheet (Resin Cupper Film: RCF), isprepared. Core base material 211 is preferred to be of a size largeenough to produce multiple main substrates 21.

Next, conductive patterns are formed by patterning copper foils 221, 222as shown in FIG. 4B.

In the following, by conducting a piercing process, laser cut or thelike, openings 2111 are formed as shown in FIGS. 3B and 4C to formconductive main substrates 21.

Meanwhile, when forming flex-rigid printed wiring board 31, as shown inFIG. 5A, rigid base material 312 having sufficient size to producemultiple flex-rigid printed wiring boards 31 is prepared first.

Next, as shown in FIG. 5B, rectangular opening 401 for arrangingflexible base material 311 and opening 402 for forming through-hole 325are formed in rigid base material 312.

Next, conductive pattern 324 and through-hole 325 are formed by copperplating and patterning as shown in FIG. 5C.

Then, flexible substrate 13 having conductive patterns 321, 322 formedon both surfaces of flexible base material 311 is arranged in opening401 as shown in FIG. 5D.

Then, as shown in FIG. 5E, flexible base material 311 and rigid basematerial 312 are covered by prepregs 403, 404, and pressed as shown inFIG. 5F. Furthermore, the resin contained in prepregs 403, 404 is cured.

Then, as shown in FIG. 5G, via holes 405 are formed in cured prepregs403, 404 by beaming a laser or the like. Then, the entire surfaces areplated and patterned to form conductive patterns 326 and filled vias327, 335 as shown in FIG. 5H.

Then, as shown in FIG. 5I, upper-layer prepregs 406, 407 are disposed,on which the same process is conducted as above to cover flexiblesubstrate 13 and rigid base material 312, and then to form upper-layerconductive patterns 326 and filled vias 327, 338. Accordingly, structure371 is formed.

By doing so, as shown in FIG. 3C, multiple structures 371 are formed ona sheet of rigid base material 312.

Then, each structure 371 is cut out.

In the following, main substrates 21 and structures 371 are eachinspected to select defect-free combinations. Then, as shown in FIGS. 3Dand 6A, defect-free structure 371 is arranged in opening 2111 adjacentto defect-free main substrate 21.

Then, as shown in FIG. 6B, prepregs 411, 412 are disposed on the top andbottom surfaces of multiple combinations of main substrate 21 andstructure 371, and pressed. Further, their resins are cured.

Then, by beaming a laser or the like, as shown in FIG. 6C, vias 413 areproperly formed in cured prepregs 411, 412. Also, through-holes 414 areformed using a drill or the like.

Then, in the areas of cured prepregs 411, 412 which will expose flexiblesubstrate 13, laser (L) is beamed as shown in FIG. 6D, then as shown inFIG. 6E, prepregs 403, 404, 406, 407, 411, 412 are cut. Then, as shownin FIG. 6F, the cut portions are removed.

Then, the entire surfaces are plated and patterned. Accordingly,multilayer wiring board 1 having the structure shown in FIG. 1 iscompleted.

As described so far, according to a multilayer wiring board of thepresent embodiment and its manufacturing method, main substrate 21 andflex-rigid printed wiring board 31 may be manufactured separately atleast to a certain step, and then a combination of the two defect-freeproducts may be put together to produce a multilayer wiring board. Thus,even if a defect occurs in main substrate 21 or flex-rigid printedwiring board 31, the entire multilayer wiring board 1 will not becomedefective, but a final product may be produced by replacing thedefective unit with a defect-free unit. Accordingly, productivityincreases compared with cases in which the entire structure ismanufactured collectively as a whole, and thus loss of material orenergy may be reduced.

Also, since the rigidity of core 211 of main substrate 21 is higher thanthat of the insulation layers of the flex-rigid printed wiring board,stresses exerted on flex-rigid printed wiring board 31 may besuppressed.

Since the wiring density of flex-rigid printed wiring board 31 is sethigher than that of the main substrate, flex-rigid printed wiring board31 may be made partially fine-pitched.

Furthermore, since main substrate 21 has no unnecessary joint sectionfor conductors, its tolerance to impact from being dropped improves.

The present invention is not limited to the above embodiment, butvarious modifications and applications may be employed.

For example, in the above embodiment, main substrate 21 and flex-rigidprinted wiring board 31 are arranged side by side; however, mainsubstrate 21 and flex-rigid printed wiring board 31 may be arranged inany way.

For example, as shown in FIG. 7, flex-rigid printed wiring board 31 maybe placed on a surface of main substrate 21. In such a case, forexample, connection pads 502 formed on a surface (the lower surface) ofrigid substrate 11 of flex-rigid printed wiring board 21 may be anchoredusing solder or the like to connection pads 501 arranged on a surface ofmain substrate 21.

Also, as shown in FIG. 8, for example, arrangement section(accommodation section) 511 may be formed in main substrate 21 toaccommodate part of rigid substrate 11 of flex-rigid printed wiringboard 31, and part of rigid substrate 11 of flex-rigid printed wiringboard 31 may be arranged in accommodation section 511. In such a case,for example, using solder or the like, connection pads 513 formed inrigid substrate 11 of flex-rigid printed wiring board 31 may be anchoredto connection pads 512 formed in accommodation section 511 of mainsubstrate 21.

Also, as shown in FIG. 9, for example, rigid substrate 11 of flex-rigidprinted wiring board 31 may be arranged to be embedded (inserted, inset)in main substrate 21. In such a case, for example, using solder or thelike, connection pads 523 formed in rigid substrate 11 of flex-rigidprinted wiring board 21 may be anchored to connection pads 522 formed inhollow section (accommodation section) 521 of main substrate 21.

Also, it is effective to manufacture flex-rigid printed wiring board 31to have such a structure as shown in FIG. 10.

Flexible substrate 13 shown in FIG. 10 has a structure formed bylaminating base material 131, conductive layers 132, 133, insulationlayers 134, 135, shield layers 136, 137 and coverlays 138, 139.

Base material 131 is formed with an insulative flexible sheet, forexample, a polyimide sheet with a thickness in the range of 20-50 μm,preferably with an approximate thickness of 30 μm.

Conductive layers 132, 133 are respectively formed on the front and backsurfaces of base material 131 and form striped conductive patterns (13a).

Insulation layers 134, 135 are formed with a polyimide film or the likewith an approximate thickness of 5-15 μm and insulate conductive layers132, 133 from the outside.

Shield layers 136, 137 are formed with a conductive layer, for example,a cured silver paste film, and shield conductive layers 132, 133 fromexternal electromagnetic noise as well as shield electromagnetic noisefrom conductive layers 132, 133 to the outside.

Coverlays 138, 139 are formed with an insulative film such as polyimidewith an approximate thickness of 5-15 μm, and insulate as well asprotect entire flexible substrate 13 from the outside.

On the other hand, rigid substrate 11 is formed by laminating firstinsulation layer 111, non-flexible base material 112, second insulationlayer 113, and first and second upper-layer insulation layers 114, 115.

Non-flexible base material 112 is to provide rigidity for rigidsubstrate 11 and is formed with a non-flexible insulative material suchas glass-epoxy resin. Non-flexible base material 112 is positionedhorizontal to flexible substrate 13 without touching it. Non-flexiblebase material 112 has substantially the same thickness as flexiblesubstrate 13, for example, in the range of 50-150 μm, preferably anapproximate thickness of 100 μm.

First and second insulation layers 111, 113 are formed by curingprepreg. First and second insulation layers 111, 113 each have athickness in the range of 50-100 μm, preferably an approximate thicknessof 50 μm.

First and second insulation layers 111, 113 cover non-flexible basematerial 112 and flexible substrate 13 from front- and back-surfacesides while exposing part of flexible substrate 13. Also, first andsecond insulation layers 111, 113 are polymerized with coverlays 138,139 on the surfaces of flexible substrate 13.

Non-flexible base material 112 and first and second insulation layers111, 113 form the core of rigid substrate 11 to support rigid substrate11 as well as to support and anchor flexible substrate 13 by sandwichingits tip.

A gap left in non-flexible base material 112, flexible substrate 13 andfirst and second insulation layers 111, 113 is filled with resin 125.Resin 125, for example, seeps out from a low-flow prepreg that formsfirst and second insulation layers 111, 113 during the manufacturingprocess and is cured to be integrated with first and second insulationlayers 111, 113.

Furthermore, in the area of second insulation layer 113 that facesconnection pad (13 b) of wiring 133 in flexible substrate 13, via (viahole, contact hole) 116 is formed.

In the area of flexible substrate 13 that faces via 116 (the area whereconnection pad (13 b) of conductive layer (13 a) is formed), shieldlayer 137 and coverlay 139 of flexible substrate 13 are removed. Via 116penetrates insulation layer 135 of flexible substrate 13 and exposesconnection pad (13 b) of conductive layer 133.

On the inner surface of via 116, conductive pattern (conductive layer)117 is formed by copper plating or the like. Conductive pattern 117 isconnected through plating to connection pad (13 b) of conductive layer133 in flexible substrate 13. Also, via 116 is filled with resin.

On second insulation layer 113, extended pattern 118 connected toconductive pattern 117 is formed. Extended pattern 118 is formed with acopper-plated layer or the like.

Also, at the edge of second insulation layer 113, namely, at theposition beyond the border of flexible base material 13 and non-flexiblebase material 112, copper pattern 124, insulated from the rest, isdisposed. Accordingly, heat generated in rigid substrate 11 may beradiated effectively.

First upper-layer insulation layer 114 is laminated on second insulationlayer 113. First upper-layer insulation layer 114 is formed by curing amaterial containing inorganic material, such as a prepreg made byimpregnating glass cloth or the like with resin. By making such astructure, tolerance to impact from being dropped may be enhanced.During the step to manufacture such a flex-rigid printed wiring board,resin from the prepreg fills via 116.

Also, on first upper-layer insulation layer 114, second upper-layerinsulation layer 115 is disposed. Second upper-layer insulation layer115 is also formed by curing a prepreg made by impregnating glass clothor the like with resin.

In first upper-layer insulation layer 114 disposed on second insulationlayer 113, via (first upper-layer via) 119 connected to extended pattern118 is formed. Via 119 is filled with conductor 120 such as copper.Also, in second upper-layer insulation layer 115 laminated on firstupper-layer insulation layer 114, via (second upper-layer via) 121connected to via 119 is formed. Via 121 is filled with conductor 122such as copper. Namely, filled built-up vias are formed by vias 119,121.

On second upper-layer insulation layer 115, conductive pattern (circuitpattern) 123 is properly formed. Via 119 is properly connected toconductive pattern 123.

The structure of the connecting area between joint section 15 andflexible substrate 13 may be such as shown in FIG. 10.

In flex-rigid printed wiring board 10 having such a structure, a tip offlexible substrate 13 is sandwiched between first and second insulationlayers 111, 113 which form the core section of rigid substrate 11, andis polymerized.

Furthermore, connection pad (13 b) of conductive layer 133 in flexiblesubstrate 13 and conductive pattern 123 of rigid substrate 11 areconnected by means of conductive pattern (copper-plated layer) 117formed inside via 116 formed in second insulation layer 113 andinsulation layer 135.

Accordingly, stresses exerted on flexible substrate 13 when flexiblesubstrate 13 is bent are not conveyed to the joint section (via 116,wiring-layer pattern 117) of rigid substrate 11. Therefore, stressesexerted on the joint section between rigid substrate 11 and flexiblesubstrate 13 are minor, resulting in high reliability.

Also, conductive layer 133 of flexible substrate 13 and conductivepattern 117 inside via 116 of rigid substrate 11 are connected throughplating. Thus, the reliability of the joint section is high.

Furthermore, the interior of via 116 is filled with resin of upper-layerinsulation layer 114. Since via 116 is anchored and supported by theresin inside via 116, the connection reliability between via 116 andconductive layer 133 is enhanced.

Also, the edges of insulation layers 113, 111 facing the flexiblesubstrate protrude beyond the edge of upper-layer insulation layer 114facing the flexible substrate. Therefore, stresses exerted on flexiblesubstrate 13 when flexible substrate 13 is bent are not passed along tothe joint section (via 116, conductive pattern 117) of rigid substrate11. Accordingly, stresses exerted on the joint section between rigidsubstrate 11 and flexible substrate 13 are minor, resulting in highreliability.

In the above example, to make understanding easier, conductive patternsare formed only on the top surfaces of rigid substrates 11, 12. However,the present invention is not limited to such. For example, as shown inFIG. 11, conductive patterns may also be disposed on the bottom side ofrigid substrates 11, 12.

In the structure shown in FIG. 11, via 141 is formed in first insulationlayer 111 and insulation layer 134 of flexible substrate 13. In theinterior of via 141, conductive pattern 142 is formed and connected toextended pattern 143 formed on first insulation layer 111. Conductivepattern 142 and extended pattern 143 are formed by patterning acopper-plated layer.

On first insulation layer 111, third and fourth upper-layer insulationlayers 144, 145 are laminated. In third and fourth upper-layerinsulation layers 144, 145, vias 146, 147 are formed respectively. Vias146, 147 are filled with conductors 148, 149. Conductive pattern 150 isformed on fourth upper-layer insulation layer 145.

The structure shown in FIG. 1, as an example in which the number ofwiring layers having conductive patterns in flex-rigid printed wiringboard 31 is greater than the number of wiring layers in a region of mainsubstrate 21 that has the same thickness as the flex-rigid substrate, anexample was shown in which the main substrate has two (2) layers andflex-rigid wiring board 31 has six (6) layers. However, the presentinvention is not limited to such. The number itself of the wiring layersin flex-rigid printed wiring board 31 and main substrate 21 is optional.For example, as shown in FIG. 12, the number of wiring layers inflex-rigid printed wiring board 31 may be set at six (6) and that ofmain substrate 21 may be set at four 4.

Also, in the above structure, an example was shown in which the numberof wiring layers having conductive patterns in flex-rigid printed wiringboard 31 is made greater than the number of wiring layers in a region ofmain substrate 21 that has the same thickness as flex-rigid printedwiring board 31. Another example was also shown in which the existingdensity of conductive patterns on the insulation layers of flex-rigidprinted wiring board 31 is made higher than the existing density ofconductive patterns on the insulation layers of main substrate 21.However, the present invention is not limited to such. As shown in FIG.12, the average number of vias per insulation layer formed in theflex-rigid printed wiring board may be set greater than the averagenumber of vias per insulation layer of main substrate 21.

For example, in the above embodiment, during a manufacturing process,opening 211 is formed so as to fit into part of main substrate 21 asshown in FIG. 3B; then main substrate 21 and part of structure 371 areput together as shown in FIG. 3D. The present invention is not limitedto such. For example, main substrate 21 and structure 371 may bearranged as shown in FIG. 13B. The manufacturing process after arrangingin such a way is the same as in the above embodiment.

For example, during a manufacturing step in the above embodiment, to usethe substrate effectively, adjacent main substrates are lined up to facein opposite directions and openings 211 are arranged alternately asshown in FIGS. 3A, 3B, 3D, 13A and 13B. Accordingly, main substrates 21and structures 371 are put together densely. The present invention isnot limited to such. For example, as shown in FIGS. 14A and 14B,multiple main substrates 21, multiple openings 211 and multiplestructures 371 may be arranged regularly to face the same direction.

Also, the method for connecting main substrate 21 and flex-rigid wiringboard 31 is optional as well. For example, a procedure such as thefollowing may also be conducted: connection pad 541 is arranged on mainsubstrate 21 as shown in FIG. 15, joint section 15 of flex-rigid wiringboard 31 is placed on connection pad 541 as shown in FIG. 16, andconnection pad 541 and connection pad 538 on joint section 15 areconnected as shown in FIG. 17.

Also, the process to manufacture multilayer wiring board 1 is notlimited to the above embodiment, but may be modified. For example, amanufacturing process may also be employed in which flex-rigid wiringboard 31 is completed first and then is put together with main substrate21.

In such a case, for example, after structure 371 shown in FIG. 5I iscompleted, laser (L) is beamed, for example, as shown in FIG. 18A, tocut unnecessary portions of prepregs 403, 404, 406, 407. At that time,flex-rigid printed wiring board 31 as shown in FIG. 2B may also becompleted after flex-rigid printed wiring board 31 is separated from itssurroundings and then the unnecessary portions of the prepregs areremoved.

In such a case, then, flex-rigid wiring board 31 is arranged in opening2111 adjacent to defect-free main substrate 21 as shown in FIG. 18B. Inthe following, it is preferred that separators 409, 410 be disposed onthe top and bottom surfaces of flexible substrate 13 in flex-rigidprinted wiring board 31 as shown in FIG. 18B. Then, as shown in FIG.18B, prepregs 411, 412 are disposed on the top and bottom surfaces ofmultiple combinations of main substrate 21 and structure 371, andpressed. Furthermore, the resin is cured.

Then, by beaming a laser or the like, vias 413 are properly formed incured prepregs 411, 412 as shown in FIG. 18D. Also, through-hole 414 isformed using a drill or the like.

In the following, laser (L) is beamed at the portions of cured prepregs411, 412, which correspond to the edges of separators 409, 410 to cutprepregs 411, 412 as shown in FIG. 18F. Then, cut portions of prepregs406, 407 and separators 409, 410 are removed.

Then, by plating on the entire structure and patterning it, multilayerwiring board 1 with the structure shown in FIG. 1 is completed.

Manufacturing productivity may also be increased in such modificationsand applications, compared with cases in which the entire structure ismanufactured collectively as a whole, and loss of material or energy maybe reduced.

In the above embodiment, joint section 15 is arranged in flex-rigidwiring board 31. However, conductors 321, 322 on flexible substrate 13may be directly connected to other circuits without arranging jointsection 15.

A wiring board according to one embodiment of the present inventionincludes the following: a wiring board is made up of a main substratehaving a conductive pattern formed on a base material, and a flex-rigidprinted wiring board structured with at least a rigid substrate and aflexible substrate connected to each other, which is arranged in themain substrate and has a conductive pattern formed on at least eitherthe rigid substrate or the flexible substrate; and the conductivepattern of the main substrate is electrically connected to theconductive pattern of the flex-rigid printed wiring board.

The conductive pattern of the flex-rigid printed wiring board iselectrically connected to, for example, a surface of the conductivepattern formed on the main substrate.

For example, at least part of the flex-rigid printed wiring board isinserted in the main substrate, and the conductive pattern of the mainsubstrate and the conductive pattern of the flex-rigid printed wiringboard are electrically connected at the insertion point.

For example, at least part of the flex-rigid wiring board is embedded inthe main substrate, and the conductive pattern of the main substrate andthe conductive pattern of the flex-rigid printed wiring board areelectrically connected at the embedded point.

The flex-rigid printed wiring board has, for example, a flexible basematerial having a conductive pattern, a non-flexible base materialpositioned horizontal to the flexible base material, an insulation layercovering at least part of the flexible base material and at least partof the non-flexible base material while exposing at least part of theflexible base material, and a conductive pattern formed on theinsulation layer. The conductive pattern of the flexible base materialand the conductive pattern on the insulation layer are connected throughplating.

The flex-rigid printed wiring board has, for example, a flexible basematerial having a conductive pattern, a non-flexible base materialpositioned horizontal to the flexible base material, and an insulationlayer covering at least part of the flexible base material and at leastpart of the non-flexible base material while exposing at least part ofthe flexible base material. A via is formed in the insulation layer anda conductive pattern is formed on the insulation layer. The conductivepattern on the insulation layer is connected to the conductive patternof the flexible base material through the via.

The flex-rigid printed wiring board has, for example, a flexible basematerial having a conductive pattern and a protective layer covering theconductive pattern, a non-flexible base material positioned horizontalto the flexible base material, an insulation layer covering at leastpart of the flexible base material and at least part of the non-flexiblebase material while exposing at least part of the flexible basematerial, and a conductive pattern formed on the insulation layer. Theconductive pattern of the flexible base material and the conductivepattern on the insulation layer are connected to the conductive patternof the flexible base material through a via formed in the insulationlayer and the protective layer.

For example, the number of layers of conductive patterns in the rigidsection of the flex-rigid printed wiring board is set greater than thenumber of layers of conductive patterns in the area of the mainsubstrate that has the same thickness as the rigid section of theflex-rigid printed wiring board.

For example, in the main substrate, multiple conductive patterns arelaminated with insulation layers in between, and vias are formed in theinsulation layers to connect the conductive patterns with each other. Inthe flex-rigid wiring board, multiple conductive patterns are laminatedwith insulation layers in between, vias are formed in the insulationlayers to connect the conductive patterns with each other, and theexisting density of conductive patterns is set higher than that in themain substrate. The average number of vias per insulation layer formedin the flex-rigid printed wiring board is set greater than the averagenumber of vias per insulation layer of the main substrate.

For example, the existing density of conductive patterns on theinsulation layers of the flex-rigid substrate is set higher than theexisting density of conductive patterns on the insulation layers of themain substrate.

A method for manufacturing a wiring board according to one embodiment ofthe present invention includes a step to form a main substrate having aconductive pattern formed on a base material; a step to form aflex-rigid printed wiring board structured with at least a rigidsubstrate and a flexible substrate connected with each other, which isarranged in the main substrate and has a conductive pattern formed on atleast either the rigid substrate or the flexible substrate; and a stepto electrically connect the conductive pattern of the main substrate andthe conductive pattern of the flex-rigid printed wiring board.

For example, the step to form a main substrate includes a step to form aconnection pad on a surface of the main substrate; the step to form aflex-rigid printed wiring board includes a step to form a connection padon a surface of the flex-rigid printed wiring board; and the connectionstep includes a step to connect the connection pad of the main substrateand the connection pad of the flex-rigid printed wiring board byarranging the flex-rigid printed wiring board on the main substrate.

For example, the step to form a main substrate includes a step to forman inset section at a surface of the main substrate to inset theflex-rigid printed wiring board and to form a connection pad in theinset section; the step to form a flex-rigid printed wiring boardincludes a step to form a connection pad on a surface of the flex-rigidprinted wiring board; and the connection step includes a step to insetpart of the flex-rigid printed wiring board in the inset section of themain substrate and to connect the connection pad of the main substrateand the connection pad of the flex-rigid printed wiring board.

For example, the step to form a main substrate includes a step to forman embedding section at a surface of the main substrate to embed theflex-rigid printed wiring board and to form a connection pad in theembedding section; the step to form a flex-rigid printed wiring boardincludes a step to form a connection pad on a surface of the flex-rigidprinted wiring board; and the connection step includes a step to embedthe flex-rigid printed wiring board in the embedding section of the mainsubstrate and to connect the connection pad of the main substrate andthe connection pad of the flex-rigid printed wiring board.

For example, the step to form a flex-rigid printed wiring board includesa step to arrange a flexible base material having a conductive patternside by side with a non-flexible base material; a covering step to coverwith an insulation layer at least part of the flexible base material andat least part of the non-flexible base material while exposing at leastpart of the flexible base material; a step to form a conductive patternon the insulation layer; and a step to connect through plating theconductive pattern of the flexible base material and the conductivepattern on the insulation material.

For example, the following steps may also be conducted: a step toposition a flexible base material having a conductive pattern to behorizontal to a non-flexible base material; a step to arrange aninsulation layer to cover at least part of the flexible base materialand at least part of the non-flexible base material while exposing atleast part of the flexible base material; a step to form a via in theinsulation layer; and a step to connect the conductive pattern on theinsulation layer and the conductive pattern of the flexible basematerial through the via.

For example, the flex-rigid printed wiring board has a step to arrange aflexible base material, which has a conductive pattern and a protectivelayer covering the conductive pattern, to be horizontal to anon-flexible base material; a step to form an insulation layer to coverat least part of the flexible base material and at least part of thenon-flexible base material while exposing at least part of the flexiblebase material; a step to form a via in the insulation layer and theprotective layer; and a step to connect through the via the conductivepattern of the flexible base material and the conductive pattern on theinsulation layer.

For example, the number of layers of conductive patterns in the rigidsection of the flex-rigid printed wiring board is set greater than thenumber of layers of conductive patterns in a region of the mainsubstrate that has the same thickness and size as the rigid section ofthe flex-rigid printed wiring board.

For example, in the main substrate, multiple conductive patterns arelaminated with insulation layers in between and vias are formed in theinsulation layers to connect the conductive patterns with each other. Inthe flex-rigid insulation layers, multiple conductive patterns arelaminated with insulation layers in between, vias are formed in theinsulation layers to connect the conductive patterns with each other,and the existing density of conductive patterns is set higher than thatin the main substrate. The average number of vias per insulation layerformed in the flex-rigid printed wiring board is set greater than theaverage number of vias per insulation layer in the main substrate.

For example, the existing density of conductive patterns on theinsulation layers of the flex-rigid substrate is set higher than theexisting density of conductive patterns on the insulation layers of themain substrate.

According to a wiring board having the above structure and itsmanufacturing method, main substrates and flex-rigid substrates may bemanufactured separately and then put together. As a result, productivitymay be maintained at a high level.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed is:
 1. A wiring board comprising: a main substratehaving a base material and a conductive pattern formed on the basematerial; a flex-rigid printed wiring board having an end portionpositioned beside the main substrate and having a rigid substrate and aflexible substrate connected to each other, the end portion beingconnected to the rigid substrate by the flexible substrate, and theflex-rigid printed wiring board having a conductive pattern formed on asurface of the end portion of the flex-rigid printed wiring board; andan insulation layer formed over the conductive pattern of the mainsubstrate and the conductive pattern of the flexible-rigid wiring board,the insulation layer having a plurality of via conductors formed throughthe insulation layer and a conductive pattern formed on the insulationlayer and directly connecting the via conductors, wherein the pluralityof via conductors includes a via conductor connected to the conductivepattern of the main substrate and a via conductor connected to theconductive pattern formed on the surface of the end portion of theflex-rigid printed wiring board such that the conductive pattern of themain substrate is electrically connected to the conductive pattern ofthe flex-rigid printed wiring board through the conductive patternformed on the insulation layer.
 2. The wiring board according to claim1, wherein the flexible substrate comprises a flexible base material anda conductive pattern, the rigid substrate comprises a non-flexible basematerial positioned horizontal to the flexible base material of theflexible substrate, the flex-rigid printed wiring board furthercomprises an insulation layer covering at least a portion of theflexible base material and at least a portion of the non-flexible basematerial while exposing at least a portion of the flexible basematerial, and a conductive pattern formed on the insulation layer of theflex-rigid printed wiring board, and the conductive pattern of theflexible substrate and the conductive pattern on the insulation layerare connected through plating.
 3. The wiring board according to claim 1,wherein the flexible substrate comprises a flexible base material and aconductive pattern, the rigid substrate comprises a non-flexible basematerial positioned horizontal to the flexible base material of theflexible substrate, the flex-rigid printed wiring board furthercomprises an insulation layer covering at least a portion of theflexible base material and at least a portion of the non-flexible basematerial while exposing at least a portion of the flexible basematerial, a via structure formed in the insulation layer of theflex-rigid printed wiring board, and a conductive pattern formed on theinsulation layer of the flex-rigid printed wiring board, and theconductive pattern on the insulation layer of the flex-rigid printedwiring board is connected to the conductive pattern of the flexiblesubstrate through the via structure.
 4. The wiring board according toclaim 1, wherein the flexible substrate comprises a flexible basematerial, a conductive pattern and a protective layer covering theconductive pattern, the rigid substrate comprises a non-flexible basematerial positioned horizontal to the flexible base material of theflexible substrate, the flex-rigid printed wiring board furthercomprises an insulation layer covering at least a portion of theflexible base material and at least a portion of the non-flexible basematerial while exposing at least a portion of the flexible basematerial, a conductive pattern formed on the insulation layer of theflex-rigid printed wiring board, and a via structure formed in theinsulation layer of the flex-rigid printed wiring board and theprotective layer, the conductive pattern of the flexible substrate andthe conductive pattern on the insulation layer of the flex-rigid printedwiring board are connected through the via structure.
 5. The wiringboard according to claim 1, wherein the conductive pattern in theflex-rigid printed wiring board is formed in a plurality of layers, theconductive pattern in the main substrate is formed in a plurality oflayers, the layers of the conductive pattern in the flex-rigid printedwiring board is set to have a greater number of layers than the layersof the conductive pattern formed in an area of the main substrate thathas a same thickness as the flex-rigid printed wiring board.
 6. Thewiring board according to claim 1, wherein the main substrate comprisesa plurality of insulation layers, a plurality of conductive patternslaminated between the insulation layers of the main substrate, and aplurality of via structures formed in the insulation layers of the mainsubstrate and connecting the conductive patterns of the main substrate,the flex-rigid printed wiring board comprises a plurality of insulatinglayers, a plurality of conductive patterns laminated between theinsulation layers of the flex-rigid printed wiring board, and aplurality of via structures formed in the insulation layers of theflex-rigid printed wiring board and connecting the conductive patternsof the flex-rigid printed wiring board, and the plurality of conductivepatterns in the flex-rigid printed wiring board has an existing densitywhich is set higher than an existing density of the plurality ofconductive patterns in the main substrate, and the plurality ofinsulation layers in the flex-rigid printed wiring board has an averagenumber of via structures per layer which is set greater than an averagenumber of via structures per layer of the plurality of insulation layersin the main substrate.
 7. The wiring board according to claim 1, whereinthe main substrate comprises a plurality of insulation layers, aplurality of conductive patterns laminated between the insulation layersof the main substrate, and a plurality of via structures formed in theinsulation layers of the main substrate and connecting the conductivepatterns of the main substrate, the flex-rigid printed wiring boardcomprises a plurality of insulating layers, a plurality of conductivepatterns laminated between the insulation layers of the flex-rigidprinted wiring board, and a plurality of via structures formed in theinsulation layers of the flex-rigid printed wiring board and connectingthe conductive patterns of the flex-rigid printed wiring board, and theplurality of conductive patterns in the flex-rigid printed wiring boardhas an existing density which is set higher than an existing density ofthe plurality of conductive patterns in the main substrate.
 8. A methodfor manufacturing a wiring board, comprising: forming a main substratehaving a base material and a conductive pattern formed on the basematerial; forming a flex-rigid printed wiring board having an endportion provided beside the main substrate and comprising a rigidsubstrate and a flexible substrate connected with each other, the endportion being connected to the rigid substrate by the flexiblesubstrate, and the flex-rigid printed wiring board having a conductivepattern formed on a surface of the end portion of the flex-rigid printedwiring board; forming an insulation layer over the conductive pattern ofthe main substrate and the conductive pattern of the flexible-rigidwiring board; forming a plurality of via conductors through theinsulation layer including a via conductor connected to the conductivepattern of the main substrate and a via conductor connected to theconductive pattern formed on the surface of the end portion of theflex-rigid printed wiring board; and forming on the insulation layer aconductive pattern directly connecting the via conductors such that theconductive pattern of the main substrate is electrically connected tothe conductive pattern formed on the surface of the end portion of theflex-rigid printed wiring board through the conductive pattern formed onthe insulation layer.
 9. The method for manufacturing a wiring boardaccording to claim 8, wherein the forming of the flex-rigid printedwiring board comprises arranging a flexible base material having aconductive pattern to be horizontal to a non-flexible base material,providing an insulation layer to cover at least a portion of theflexible base material and at least a portion of the non-flexible basematerial while exposing at least a portion of the flexible basematerial, forming a conductive pattern on the insulation layer of theflex-rigid printed wiring board, forming a via structure in theinsulation layer of the flex-rigid printed wiring board, and connectingthrough the via structure the conductive pattern on the insulation layerand the conductive pattern of the flexible base material.
 10. The methodfor manufacturing a wiring board according to claim 8, wherein theforming of the flex-rigid printed wiring board comprises arranging aflexible base material having a conductive pattern and a protectivelayer covering the conductive pattern to be horizontal to a non-flexiblebase material, forming an insulation layer to cover at least a part ofthe flexible base material and at least a portion of the non-flexiblebase material while exposing at least a portion of the flexible basematerial, forming a conductive pattern on the insulation layer of theflex-rigid printed wiring board, forming a via structure in theinsulation layer of the flex-rigid printed wiring board and theprotective layer, and connecting through the via structure theconductive pattern of the flexible base material and the conductivepattern on the insulation layer.
 11. The method for manufacturing awiring board according to claim 8, further comprising setting a numberof layers of conductive patterns in the flex-rigid printed wiring boardto be greater than a number of layers of conductive patterns in a regionof the main substrate that has a same thickness and size as theflex-rigid printed wiring board, wherein the forming of the mainsubstrate comprises forming the layers of the conductive patterns in themain substrate, and the forming of the flex-rigid printed wiring boardcomprises forming the layers of the conductive patterns in theflex-rigid printed wiring board.
 12. The method for manufacturing awiring board according to claim 8, further comprising setting anexisting density of conductive patterns in the flex-rigid printed wiringboard to be higher than an existing density of conductive patterns inthe main substrate, and setting an average number of via structures perlayer of insulation layers formed in the flex-rigid printed wiring boardto be greater than an average number of via structures per layer ofinsulation layers in the main substrate, wherein the forming of the mainsubstrate comprises forming the insulation layers, the conductivepatterns laminated between the insulation layers, and the via structuresformed in the insulation layers and connecting the conductive patternsin the main substrate, and the forming of the flex-rigid printed wiringboard comprises forming the insulation layers, the conductive patternslaminated between the insulation layers, and the via structures formedin the insulation layers and connecting the conductive patterns in theflex-rigid printed wiring board.
 13. The method for manufacturing awiring board according to claim 8, further comprising setting anexisting density of conductive patterns on insulation layers in theflex-rigid substrate to be higher than an existing density of conductivepatterns on insulation layers of the main substrate, wherein the formingof the main substrate comprises forming the insulation layers and theconductive patterns laminated between the insulation layers, and theforming of the flex-rigid printed wiring board comprises forming theinsulation layers and the conductive patterns laminated between theinsulation layers.
 14. The wiring board of claim 1, wherein the mainsubstrate has greater rigidity than the end portion of theflexible-rigid wiring board.
 15. The method for manufacturing a wiringboard according to claim 8, further comprising: providing said basematerial of the main substrate having a predetermined rigidity; andproviding said end portion of the flex-rigid printed wiring board havinga rigidity less than said rigidity of the base material of the mainsubstrate.